Home shopping by use of the television has been growing in popularity in recent years. Generally, home shopping channels are transmitted on a community antenna television (CATV) facility. The CATV facility, which has the capacity for transmitting a large number of commercial and public television signals, is usually connected to homes via a network of coaxial cables. In most of the home shopping systems being offered to date, subscribers passively view the home shopping channel, watch items and pricing being presented by television sales people, and if interested in a particular item, place an order over the telephone or by mail. Similarly, televised real estate offerings which present still-video pictures and information about homes for sale in a particular area are also becoming a popular method of communicating such information to a mass audience. These systems are non-interactive, in the sense that a viewer may passively watch items as they are presented on the television screen, but cannot control the course of the presentation.
More advanced interactive systems have been designed and implemented, wherein viewers are able to request a display of particular items in which they have an interest, and can control their information retrieval or perform individualized shopping as they proceed. A system of this sort is described in U.S. Pat. No. 4,734,764, entitled "Cable Television System Selectively Distributing Pre-Recorded Video and Audio Messages". This prior art invention describes a system which conveys still-frame television-quality video with overlaid graphics information and an audio message (when appropriate), to a multiplicity of CATV subscribers who tune to a specific cable channel. The subscriber, by use of a Touch-Tone telephone, transmits particular codes in response to message prompts which are displayed in menu form on the TV screen, and is able to request video displays and information on specific products as well as make purchases. The user of this system requires no additional equipment at his location other than a Touch-Tone telephone and a television set.
In order to interactively operate this type of prior art system, a subscriber tunes to the CATV channel which is being used for transmission, and dials a telephone number to gain access to the system. Each subscriber is given a particular identification number upon subscribing to the service. When this identifying number is entered via the Touch-Tone telephone keypad, the system recognizes the subscriber and his location. Graphic overlays which depict menus and directories of "electronic stores" that are on the system are then displayed, and by responding to these menus with a sequence of keystrokes on the Touch-Tone telephone keypad, the subscriber may, by means of selected video images, enter and browse through a particular store of his choice (or follow other shopping paradigms such as going down a particular aisle in a supermarket), select a particular product of interest, make purchases or request additional information or help. By selecting from a list of menu prompts which are displayed on the television screen, and which the subscriber enters on the Touch-Tone keypad, his television screen displays still-frame video, having overlaid graphics where appropriate, and possibly accompanied by a sound track that presents information about the requested item.
This prior art system uses a CATV cable network to transmit the requested video presentations and accompanying audio messages to its subscribers. In conventional television transmission, video images are transmitted at the rate of 30 frames per second (the North American or Japanese standard), or 25 frames per second (the European standard). A video frame is an interleaved composition of two video fields, with each video field being further composed of a plurality of scan lines which contain the video image information and a smaller plurality of scan lines referred to as the "vertical blanking interval". The interactive system described in U.S. Pat. No. 4,734,764 makes use of the vertical blanking interval (which consists of the first 21 lines of the video field) to store information which identifies the particular subscriber's reception device to which the requested video images and audio commentary are addressed. The control center of the CATV system (the CATV headend) transmits the frames of video and audio data, with this addressing information encoded in the vertical blanking interval, along the main "trunk" coaxial cables of the system in analog form. In order to compensate for signal losses which naturally occur as a result of transmission, CATV cable systems utilize amplifiers positioned at various locations downstream from the control center. At each of these locations, the signals from the control center are amplified and further transmitted down a plurality of secondary distribution cables. At points along the secondary distribution cables are "taps", at which the signals are split into a plurality of "drop" cables which terminate at subscriber's television sets.
To accommodate a large number of concurrent subscribers, the interactive system described in U.S. Pat. No. 4,734,764 utilizes a reception device known as a frame store unit, or "frame grabber", typically located near each amplifier of the distribution system. Each frame store unit services a small number of cable drops, and functions to capture the information that is destined for a subscriber whose particular identification code, encoded in the vertical blanking interval, matches an identification code associated with the frame store unit. The video and audio information is transmitted to the frame store unit on two separate channels. The frame store unit captures the analog video and audio information which has the appropriate address encoded in the vertical blanking interval of the frames and stores the information into its memory. The frame store unit then replays the stored video information 30 times per second (according to the U.S. National Television Standards Committee (NTSC) requirement), and transmits the video along with any accompanying audio message to the particular subscriber that it is servicing.
In the prior art system of U.S. Pat. No. 4,734,764, which has been briefly described above, the video and audio presentation which comprises a particular merchandise offering by a commercial client, must first be prepared and encoded onto conventional laser video discs. A plurality of conventional video disc players at the central system site comprise the data storage and playback portion of a subsystem which transmits the appropriate video and audio information in analog form, under control of a central processing unit. The video information is time-multiplexed in the proper sequence, and the audio is appropriately modulated and frequency-division multiplexed for transmission down the CATV cable network.
Numerous problems and limitations are associated with this type of "analog" interactive system, even though the small amount of data that is generated may be transmitted with a link having much less bandwidth. First, a large number of video disc players are required, making the physical size of the electronics for this prior art system cumbersome. Adding to this cost is the utilization of a full bandwidth telephone link for each connection between a subscriber and the host computer of the system, even though the small amount of data that is generated may be transmitted with a link having much less bandwidth. Second, the response time between a subscriber entering a particular code on the telephone keypad and the appearance of a display in response to that code is too slow to establish a comfortable interactive session. The response time in the analog system is limited primarily by the time it takes the video disc player to access a particular location on the disc and can be on the order of several seconds. The slow response time may be exacerbated by the graphics overlay process, in which a graphics decoder receives graphics information that is associated with a particular video frame from the central processing unit, generates the appropriate graphics display data and routes this data to a video combiner. The video combiner must first receive the video frame from the video player and then overlay the graphics information onto the frame.
Further, in the prior art analog system, the audio information is stored on the video disc in the electronic format of a video frame, each frame holding a maximum of ten seconds of audio. This imposes a costly buffering requirement needed to accommodate longer segments of audio during playback. In many cases, this time limitation is too restrictive for practical use. In other cases it is wasteful of space.
An additional limitation arises from the choice of a laser disc as the storage medium for the video and audio data. A commercial client who desires to market his merchandise or services on the interactive system of the prior art must undertake a lengthy premastering procedure, required to convert his advertising material (possibly in the format of catalog photographs, video tape information, etc.) into a format which can be encoded onto a video disc master. Multiple copies of the master disc must then be made so that each video disc player in the system can have a copy of the information when it is called upon to deliver a particular presentation to a subscriber. This premastering and duplication process is a time-consuming, linear and batch-oriented procedure, generally taking up to 10 weeks from initial setup to final product. The process provides no mechanism for making minor modifications to audio or video images at a later date. If changes are required, a new video disc must be mastered and reproduced. Thus, no reusable archiving is possible.
The prior art analog system is structured with an overly complicated pathway between the subscriber and host computer system which does not generate adequate feedback to either the subscriber or the system. For example, when a subscriber enters a particular sequence of keystrokes, he has no acknowledgment that the sequence has been properly received by the system. Similarly, the system has no feedback that a subscriber has received whatever was transmitted to him. Further, when help from a consumer service representative is requested by a subscriber, the consumer service representative can hear what the subscriber is saying over the telephone, but cannot see what is being displayed on the subscriber's TV screen.
Another important drawback of the prior art system is the manner in which the analog data is distributed from the system to the CATV center and the subscribers. The cost of transmitting data from the host computer to the CATV is expensive and the prior art system makes sub-optimal use of the distribution channel capacity. In the prior art system, the video information is time-multiplexed onto one distribution channel while the audio is frequency-division multiplexed onto another distribution channel. Thus, the CATV headend must allocate two distribution channels to the system. Not only are these channels costly to acquire, but many CATV companies may not have enough channel capacity for all their users, and from a business perspective, may be hesitant to sell more than one channel to a single user.
Finally, the prior art system has problems which are fundamentally related to the storing, copying and transmission of data in analog form. Analog signals are more prone to degradation by noise sources that generally arise in any electronic system. Degradation of analog signals as they are transmitted down the long lengths of coaxial line which comprise the transmission network of the CATV system is inevitable. Additionally, the maximum signal-to-noise of the video signals which are attainable at the output of a video disc player is much lower than the noise figure for studio quality video broadcast. This adds to the degradation in quality of the final video images seen by the subscriber.